DESCRIPTION: Inflammatory diseases are a major cause of morbidity and mortality. They are characterized by rapid recruitment of inflammatory cells which requires the concerted action of chemoattractants, cytokines and adhesion molecules. E, P and L-selectins have been shown to mediate leukocyte rolling and to be required for the recruitment of inflammatory cells in vivo. This is illustrated by the moderate inflammatory defects seen in mutant mice lacking a single selectin gene, and in the severe inflammatory defects seen in mice lacking both E and P-selectin. The PI has previously determined the sequential and partially overlapping role of P and L-selectin in trauma and cytokine-induced leukocyte rolling, identified the uniquely slow leukocyte rolling mediated by E-selectin in vivo, mapped the expression of the endothelial selectins in vivo, and determined the extent and importance of transient leukocyte deformation during rolling. The hypothesis of this proposal is that the selectins serve partially overlapping, but distinguishable functions in leukocyte recruitment in vivo. It is proposed that L-selectin mainly mediates leukocyte capture, including interaction of flowing leukocytes with other, already adherent leukocytes, P-selectin mediates both capture and rolling, and E-selectin mediates slow rolling leading to firm adhesion. The specific aims are to: (1) define the mode of initiation of leukocyte-endothelial interaction when adherent leukocytes are already present, (2) unmask the independent contribution of L-selectin to leukocyte rolling in vivo, (3) compare the shear resistance of P-selectin and E-selectin dependent rolling, (4) determine whether function-blocking antibodies to PSGL-1 (P-selectin Glycoprotein Ligand-1) can block P-selectin dependent rolling, and (5) compare the number of leukocytes becoming adherent in response to chemoattractants in wild type and E-selectin deficient mice. The investigations will use intravital microscopy in the cremaster muscle microcirculation of mice deficient in for one or more selectins. The mice will be injected with function-blocking monoclonal antibodies to relevant adhesion molecules to isolate the function of each selectin. The knowledge gained will improve the understanding of the inflammatory process and provide significant information pertinent to the development of potential anti-inflammatory therapies for future clinical use in patients.